Tomado de Wikipedia:
[edit] PEN fiber (Pentex)
PEN (
Polyethylene naphthalate), commonly known by Honeywell's trade name "Pentex", is another kind of polyester fiber, which stretches only 40% as much as standard PET fibers, but about twice as much as Kevlar 29. Because it only shrinks about a third as much as a good PET, PEN can not be woven as tightly; thus, woven PEN must be impregnated with resin making sails prone to damage from improper use and handling. PEN is better suited for making laminated sailcloth, where the fibers are laid straight for strength and are bonded to sheets of film for stability (e.g.,
PET film often called by one of its trade names Mylar), or as a
taffeta outer layer of a laminate, protecting a PET film. PEN laminates are an economical alternative for higher performance sail.